This invention relates in general to the monitoring of a workpiece being surface treated by impingement of a focused laser beam thereon, and more particularly to monitoring of a laser beam etching operation on the surface of a wafer type workpiece.
The use of a laser beam to etch the surface of a small workpiece, such as a semi-conductor wafer, is already well known as well as the monitoring of the etch rate. The use of a relatively low intensity light transmitted to a target along the path of a laser beam for illumination of the target surface being treated by the laser beam is also known. In connection with very small workpieces, however, direct visual observance of the workpiece for monitoring purposes and for precise positional control of the laser beam focus spot, presents a special problem to which the prior art is not specifically addressed.
It is therefore an important object of the present invention to provide a device through which precise positioning of a laser beam spot on a wafer surface is made possible for reproducible etching purposes by accurate measurement of etch rate and visual image display monitoring.